Is there a maintanance fee for the use of GPS?

No, the usage of the GPS is free of charge for everyone, worldwide.

The Global Positioning System (GPS) is a space-based global navigation satellite system that provides reliable location
and time information in all weather and at all times and anywhere on or
near the Earth where there is an unobstructed line of sight to four or
more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver.